1. Field of the Invention
The present invention relates to a system and method for capturing the shape of a dento-maxillofacial object out of volumetric image data of that object. Further, the present invention relates to a system and method for determining a parameter for use in digitizing the dento-maxillofacial object.
2. Description of the Related Technology
Dento-maxillofacial treatments are related to the dentition, the skull and the facial soft tissues. The scope of the treatments goes from handling teeth—such as aligning, restoring crowns, extracting, restoring including root and crown—over bone related treatments—such as maxillofacial surgery involving surgical remodelling or restoring of the skull and dentition, encompassing surgical interventions of repair, in particular, of a mis-positioning of the jaws with respect to one another, called orthognathic surgery, temporomandibular joint (TMJ) treatments—over facial soft tissue treatments—such as tissue sculpting, lifting, and so forth. Important in these treatments is creating a good occlusion and smile line. With ‘occlusion’ is meant the manner in which the teeth from the upper and lower arches come together when the mouth is closed.
Since dento-maxillofacial treatments are complex and have a big impact on the patient's facial outlook, accurate treatment planning is required. Computer aided dento-maxillofacial planning systems are becoming available which digitize the traditional manual treatment planning process. In order to be able to optimize the treatment plan, it is often necessary to incorporate in these systems a digitized version of dento-maxillofacial objects, such as dental impressions, dental stone models or removable prostheses, etc. Consequently, a need exists in some cases to enable accurate digitization of dento-maxillofacial objects.
Dento-maxillofacial objects are characterized by a highly irregular shape showing various undercuts and small details. This characteristic makes digitizing the shape a challenging task.
To digitize dento-maxillofacial objects, surface scanning based on stereo-imaging, structure light imaging, laser scanning or, amongst others, conoscopic holography can be applied. These methods can provide highly detailed surface scans of the objects. Although some techniques are more flexible with respect to the variety of shapes they can scan, certain shapes remain difficult to digitize.
An alternative method to digitize the shape of the dento-maxillofacial material is using volumetric imaging techniques, such as destructive scanning or tomographic imaging. Tomographic imaging includes all image modalities that generate tomographic images. These tomographic images can be arranged in a 3D image volume.
An example of such tomographic imaging is computed tomography (CT) scanning. With this modality, X-rays are employed to digitize the shape of the dento-maxillofacial material. This is typically done in an industrialized environment based on industrial CT scanners or micro-CT scanners. However, this approach needs a significant investment and creates a logistic hassle. For example, a dental impression deforms when it dries. Therefore, it is advisable to digitize the impression as soon as possible and to carefully control the environment in which it is stored.
Although various imaging techniques exist for scanning objects, the problem remains that capturing the exact contour or the shape of the objects out of the volumetric image data is very difficult or inaccurate. Moreover, this contouring or shaping is usually performed in a subjective manner. This contouring process is often also called segmentation of the volumetric image data.
Consequently, there is a need in some cases for an accurate method to capture the shape out of volumetric image data, such as the shape of dento-maxillofacial materials in a more reliable way.
In WO00/19929 the volume imaging technique is described of destructive scanning, whereby images of slices are taken.
Document U.S. Pat. No. 7,123,767 describes techniques for segmenting a digital dentition model into models of individual components using e.g., CT scans. Several 3D segmentation techniques are described, many of which are human-assisted. Other computer-implemented techniques have a drawback that only interproximal margins are created, instead of an accurate threshold value. This document is however not concerned with the accuracy of the segmentation of a digital dentition model, even though this is a crucial factor.
There is also a need in some cases to offer dental professionals the possibility to scan dento-maxillofacial materials with volume imaging techniques, such as tomographic imaging, that are easily accessible or installed in the dental office. An example of such a tomographic imaging method is CT scanning with a standard medical CT scanner or a Cone-Beam CT scanner.
Tomographic imaging creates a volumetric image dataset, or even several ones, out of which the surface of the dento-maxillofacial object needs to be segmented. Given the large variety of tomographic imaging equipment, an easy and highly automated method may be required in order to allow convenient, accurate digitization of the shape of dento-maxillofacial objects.
The paper ‘Geometric accuracy of digital volume tomography and conventional computed tomography’ (Eggers et al., British Journal of Oral and Maxillofacial Surgery, vol. 46, no. 8, December 2008, pp. 639-644) is concerned with the question whether digital volume tomographic imaging is suitable for image-guided operating. The geometric accuracy is important for accurate patient to image registration, and so for the safety of patients, digital volume tomography is found to be an appropriate method.
European patent application EP1808129 discloses a human body information extraction device for extracting human body information including position information from a reference position, from 3D information on the human body elements obtained from a CT information or the like in which the position information from the reference position with respect to a human body element is unknown. In the proposed solution a reference plane for positioning is detected by detecting information on a common positioning member contained in both of the 3D human body information from the CT information and a 3D model information from a human body model.